For the purposes of the present disclosure, a semibright metal coating will be one which is of uniform but somewhat dull texture as can be described as "mat-gloss". A Watt's-type plating bath is one which contains nickel sulfate, nickel chloride and boric acid and, where the deposit is to consist of nickel-cobalt, a corresponding cobalt salt. Finally, the expression "nickel-containing coating" and terms of similar import are used to refer to coatings consisting of nickel or of nickel-cobalt. Reference is made to THE ENCYCLOPEDIA ELECTROCHEMISTRY, Reinhold Publishing Co., New York, 1964, page 845, inter alia in this regard.
It is known in the electrodeposition of nickel or nickel-cobalt (i.e. a nickel-containing coating) to control the finish so as to obtain a uniform semigloss layer by introducing into the plating bath a foreign inorganic solid of restricted particle size which is incorporated in the coating and appears to provide grains which create a granular appearance or serve an nuclei for the metal crystals. However, the matte effect is frequently destroyed by the roughness of the surface. When inorganic particulates are used, moreover, it is difficult, if not impossible, to create and maintain a homogeneous dispersion and hence the coating is nonuniform.
It has been proposed to avoid this disadvantage by introducing into the electrodeposition bath one or more nonionic surfactants. There materials have the disadvantage that they tend to come out of solution with increases in temperature and create an emulsion which is difficult to handle and does not always give good results from the point of view of uniform matte finish.